1. Field of the Invention
The present invention generally relates to correlation energy detectors and radio communication apparatuses, and more particularly to a correlation energy detector for detecting a magnitude of a correlation between a first signal series (Ii, Qi) described by I-Q orthogonal components and a predetermined second signal series (HJ), and to a radio communication apparatus which uses such a correlation energy detector.
The code division multiple access (CDMA) system is regarded as a mobile communication system of the next generation, and in the United States, a standardized system (N-CDMA) called IS-95 is already reduced to practice. In addition, there is a possibility of the CDMA system being applied to a semi-fixed mobile communication system called wireless local loop (WLL) as a means of infra-structure. Such a system proposed by Qualcomm of the United States is a CDMA system using a chip rate of 1.2288 Mcs, wherein a synchronous detection system using an extrapolated pilot signal is employed for the down-line, and an asynchronous detection system using the M-ary orthogonal modulation is employed for the up-line (reverse link). In the asynchronous detection system, an amplitude signal is converted into power so as to eliminate a phase error caused by fading or the like, and the communication quality or bit error rate (BER) is improved by employing the RAKE reception technique. The present invention, as will be described later, is suited for application to this kind of radio communication apparatus (reverse link).
2. Description of the Related Art
FIGS. 1 through 7, FIGS. 8A through 8C and FIG. 9 are diagrams for explaining the prior art, more particularly, the standardized system IS-95. FIG. 1 is a system block diagram showing a transmitter part of a mobile station, and FIG. 2 is a diagram showing a signal sequence of the transmitter part. Signals (A) through (E) shown in FIG. 2 are the signals (A) through (E) shown in FIG. 1.
An input information signal is subjected to a cyclic coding in a CRC operation unit 11, and is converted into an error correction code in a convolutional encoder (ENC) 12. This error correction code is subjected to an identical symbol repeating process in a symbol repeating unit 13, so as to unify the input signals in the range of 1.2 kbps to 9.6 kbps to the signal (A) of 9.6 kbps. The signal (A) is further subjected to a buffering process in an interleaver 14. A signal sequence (B) of 28.8 kbps is read from the interleaver 14 and input to an M-ary (64) orthogonal modulator 15.
The 64-ary orthogonal modulator 15 converts the 6-bit input data to a corresponding 64-bit Walsh code (C), that is, spreads the input data by 64/6 times. For example, the 6-bit input data xe2x80x9c000000xe2x80x9d is converted into a 64-bit Walsh code xe2x80x9c00000000 . . . 00000000xe2x80x9d, and the 6-bit input data xe2x80x9c000001xe2x80x9d is converted into a 64-bit Walsh code xe2x80x9c01010101 . . . 01010101xe2x80x9d. Such Walsh codes (C) are finally output from the 64-ary orthogonal modulator 15 as a signal (D) of 307.2 kcps.
A multiplier 17 multiplies to the signal (D) a PN code (user code or long code) LCD which is generated for each user by a long code generator 16. As a result, a spread code sequence (E) of 1.2288 Mcps is output from the multiplier 17 and is supplied to a multiplier 201 provided for the I-channel and a multiplier 202 provided for the Q-channel. The multiplier 201 multiplies to the spread code sequence (E) a PN code (short code) SCD for identifying the base station, which is generated from a short code generator 18 and is received via a shifter 19. On the other hand, the multiplier 202 multiplies to the spread code sequence (E) the PN code SCD which is generated from the short code generator 18.
An output of the multiplier 201 is passed through a filter 221 and a digital-to-analog (D/A) converter 231 and converted into an analog signal before being supplied to a quadrature phase shift keying (QPSK) modulator 24. An output of the multiplier 202 is passed through a xc2xd chip delay unit 21, a filter 222 and a D/A converter 232 and converted into an analog signal before being supplied to the QPSK modulator 24.
Since the xc2xd chip delay unit 21 provides a xc2xd chip shift between the I-channel and the Q-channel, an output of the QPSK modulator 24 becomes an offset QPSK (OQPSK) modulated signal. By this OQPSK modulation, no phase change of xcfx80 occurs, and the phase change becomes xcfx80/2 at the maximum. For this reason, even under an extreme band limitation, the signal envelope only dips slightly, and no zero-point occurs. An OQPSK modulated signal output from the QPSK modulator 24 is converted into a radio frequency signal in a transmitting radio frequency (RF) unit (Tx) 25 and is transmitted to the base station via an antenna A0.
FIG. 3 is a system block diagram showing a receiver part (reverse link demodulator part) of the base station. In addition, FIG. 4 is a diagram for explaining a service area of the base station, and FIG. 5 is a diagram for explaining asynchronous detection. Further, FIG. 6 is a system block diagram showing fingers forming the receiver part, and FIG. 7 is a diagram showing a signal sequence of the receiver part.
As shown in FIG. 4, 1 cell is divided into 3 sectors, and 2 reception (diversity) antennas are provided with respect to 1 sector. A maximum number of antennas capable of simultaneously communicating with a mobile station MS which is located at an arbitrary position is 4, namely, A11, A12, A21 and A22, in this particular case. Hence, 4 corresponding antennas A1 through A4 are shown in FIG. 3.
In FIG. 3, the received signals from the antennas A1 through A4 are amplified and converted into intermediate frequency signals IF in corresponding receiving RF units (Rx) 311 through 314, and demodulated into orthogonal demodulated data (I1, Q1) through (I4, Q4) in corresponding QPSK demodulators (DEM) 321 through 324. The orthogonal demodulated data (I1, Q1) through (I4, Q4) are selected by a signal selector 33 which operates under the control of a searcher 40, and input to fingers 341 through 344. In this state, the received wave is not necessarily supplied constantly to each finger, and each finger operates under conditions, such as antenna selection and delay time PNoffset, which are specified by the searcher. Hence, various combinations are actually permitted for the connection of the QPSK demodulators 321 through 324 and the fingers 341 through 344.
FIG. 6 shows the construction of the fingers 341 through 344. In a despreader 41 of the finger 341, the input demodulated data I1, Q1 are respectively despread by a correlator 42 based on the short code PNoffset (PNI1, PNQ1) supplied from the searcher 40. The short codes PNI1, PNQ1 correspond to the short code SCD of the transmitter end, and PNI1 is phase (chip) synchronized to the demodulated data I1 while PNQ1 is phase (chip) synchronized to the demodulated data Q1. Further, output data I1, Q1 of the correlator 40 are despread by corresponding multipliers 431 and 432 based on a long code LCD corresponding to the user code LCD of the transmitting end. In addition, an adder 441 adds 4 consecutive despread codes I1 from the multipliers 431, and an adder 442 adds 4 consecutive despread codes Q1 from the multiplier 432.
If no chip error occurs during the transmission, output data I1, Q1, that is, (A) shown in FIG. 7, of the adders 441 and 442 correspond to the output Walsh code of the 64-ary orthogonal modulator 15 of the transmitting end. Actually, however, the output data I1, Q1 (A) of the adders 441 and 442 do not necessarily correspond to the output Walsh code of the 64-ary orthogonal modulator 15 due to the chip error or the like introduced during the transmission.
The output data I1, Q1 (A) of the adders 441 and 442 are subjected to the Hadamard transform in corresponding fast Hadamard transform units (FHT) 451 and 452. In other words, the input data I1, Q1 and 64 kinds of Walsh code sequences are subjected to matrix operations, so that correlation values (I00 through I63), (Q00 through Q63) are generated depending on the correlation of the codes. Energy calculation units 4600 through 4663 obtain powers (I002+Q002) through (I632+Q632) for each of the correlation values, and output correlation energies E00 through E63 corresponding to Walsh code numbers 0 through 63.
The correlation energies E00 through E63 are input to a gate circuit 47 and to a maximum value selector (MXS) 48. The maximum value selector 48 selects a maximum correlation energy MXE from the correlation energies E00 through E63. A comparator (CMP) 49 compares the maximum correlation energy MXE and a predetermined threshold value TH, and closes the gate circuit 47 when MXE greater than TH and otherwise opens the gate circuit 47. In other words, the output correlation energies E00 through E63 of the energy calculation units 4600 through 4663 are output from the finger 341 and contribute to the RAKE combining at the latter stage only when the maximum energy MXE exceeds the predetermined threshold value TH. Similar operations are carried out in the other fingers 342 through 344. Under the RAKE reception system, the correlation value level is made large by combining only the correlation value outputs from the valid fingers of each of the correlation value outputs (energies) of the multi-path which includes 4 paths at the maximum in FIG. 3, so as to increase the certainty of the correlation value.
Returning now to the description of FIG. 3, the output correlation energies E00 through E63 from the fingers 341 through 344 are combined (added) for each of the correlation energies E00 through E63 in the combining units 3500 through 3563, and combined energies G00 through G63 are output from the combining units 3500 through 3563. A maximum value selector 36 selects a maximum combined energy MXG of the combined energies G00 through G63, and demodulates a Walsh code (number) MXW corresponding to this maximum combined energy MXG.
Under the asynchronous detection system, the phase component is eliminated by converting the demodulated signals I, Q into power (I2+Q2), so as to prevent phase noise caused by fading and to prevent deterioration of a local signal caused by frequency error. FIG. 5 is a diagram for explaining the asynchronous detection in this state. Even if the demodulated phase changes (rotates) by xcex94xcfx86 between timings t1 and t2, the maximum combined energy MXG=G15 is obtained at the timing t1, and the maximum combined energy MXG=G32 is obtained at the timing t2.
The Walsh code MXW, that is, (C) shown in FIG. 7, is converted into a corresponding 6-bit data, that is, (D) shown in FIG. 7, by a code converter 37, deinterleaved in a deinterleaver 38, subjected to a Viterbi decoding (error correction decoding) in a Viterbi decoder 39, and output as received data RD.
According to the conventional system described above, the finger locked state occurs when MXE greater than TH as a result of the comparison of the maximum combined energy MXE of the combined energies G00 through G63 and the predetermined threshold value TH.
FIG. 8A is a diagram showing an example of a correlation energy versus Eb/No characteristic. In FIG. 8A, the ordinate indicates the correlation energy, and the abscissa indicates Eb/No, that is, the signal-to-noise (S/N) ratio per bit. Generally, the correlation energy is high when Eb/No (reception quality) is high, and the correlation energy decreases when Eb/No decreases, as will be described hereunder.
FIG. 8B is a diagram showing an example of a case where Eb/No is sufficiently high. In FIG. 8B, the ordinate indicates the correlation energy, and the abscissa indicates energy types E00 through E63 corresponding to the Walsh code numbers W00 through W63. If Eb/No (communication quality) is sufficiently high and the Walsh code W15 sent from the transmitting end is correctly demodulated into the code W15 at the receiving end, the correlation energy E15 becomes MXE at the maximum, and the other correlation energies all become xe2x80x9c0xe2x80x9d. Accordingly, the conventional system can judge whether or not XXE greater than TH.
FIG. 8C is a diagram showing an example of a case where Eb/No decreases. In FIG. 8B, the ordinate indicates the correlation energy, and the abscissa indicates energy types E00 through E63 corresponding to the Walsh code numbers W00 through W63. If Eb/No (communication quality) decreases, burst error or the like mixes into the Walsh code W15 sent from the transmitting end, and the correlation energy E15 decreases in a received code W15xe2x80x2 which includes error and is demodulated at the receiving end. As a result, the correlation energy increases in relation to the other codes, and in the conventional system it is impossible to detect whether or not E15 greater than TH, that is, whether or not the finger locked state occurs.
FIG. 9 is a system block diagram showing a conventional searcher. In FIG. 9, those parts which are the same as those corresponding parts in FIG. 6 are designated by the same reference numerals, and a description thereof will be omitted.
In the searcher 40 shown in FIG. 9, a search controller 73 controls the signal selector 33 shown in FIG. 3, so as to select the demodulated data Ii, Qi of the desired path. In addition, the search controller 73 instructs a desired delay time with respect to a delay time adjusting part 71 and a delay time PNoffset with respect to a PN generator 74, so as to detect the maximum correlation energy MXE in this state, and detects (monitors) the path which satisfies such conditions. The construction of the despreader 41 and the structure within a correlation energy detector 72 may be the same as those described above with respect to the finger 34. However, no RAKE combining is made in the searcher 40, and thus, no combining of the finger outputs is made.
According to the conventional system, the correlation energy of the fingers are obtained in the form of a sum of squares (I2+Q2). However, the circuit scale of the multipliers for realizing the sum of squares operation is extremely large. In addition, the number of bits required to describe the correlation energy by the sum of squares is doubled as compared to normal, thereby making the circuit scale of subsequent circuit stages extremely large. Moreover, since the correlation value of the outputs of the fast Hadamard transform units (FHT) has a large dynamic range, it is difficult to reduce the number of bits without adverse effects. In other words, if the number of bits is reduced by rounding or limiting, the accuracy of the correlation value is directly affected. These problems exist not only in the main signal processing system such as the finger 34, but also in the searcher 40.
Accordingly, it is a general object to provide a novel and useful correlation energy detector and radio communication apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a correlation energy detector and a radio communication apparatus which can appropriately detect the correlation energy and appropriately combine fingers (RAKE) using a relatively simple structure.
Still another object of the present invention is to provide a correlation energy detector for detecting a magnitude of a correlation between a first signal series (Ii, Qi) described by I-Q orthogonal components and a predetermined second signal series (HJ), comprising correlation computing means for computing correlation values (Iij, Qij) between the first signal series (Ii, Qi) and the predetermined second signal series (HJ), and root computing means for computing {{square root over ( )}(Iij2+Qij2)} as a root value of a sum of squares of the correlation values (Iij, Qij) obtained from the correlation computing means. According to the correlation energy detector of the present invention, the number of bits of the root of the sum-of-squares correlation energy is greatly reduced to approximately xc2xd as compared to that of the sum of squares correlation energy. For this reason, the wiring scale and the circuit scale of the subsequent circuit stages can be reduced considerably. Furthermore, the detection accuracy of the maximum energy and the accuracy of the combined energy are substantially unaffected by the correlation energy detection, and thus, appropriate detection of the correlation energy is possible using a simple structure.
A further object of the present invention is to provide a correlation energy detector for detecting a magnitude of a correlation between a first signal series (Ii, Qi) described by I-Q orthogonal components and a predetermined second signal series (HJ), comprising correlation computing means for computing correlation values (Iij, Qij) between the first signal series (Ii, Qi) and the predetermined second signal series (HJ), and absolute value sum computing means for computing (|Iij|+|Qij|) as a sum of absolute values of the correlation values (Iij, Qij) obtained from the correlation computing means. According to the correlation energy detector of the present invention, the number of bits of the absolute value sum correlation energy is greatly reduced to approximately xc2xd as compared to that of the sum of squares correlation energy. For this reason, the wiring scale and the circuit scale of the subsequent circuit stages can be reduced considerably. In addition, it is unnecessary to provide multipliers which would be necessary if the sum of squares (Iij2+Qij2) were to be computed, and the structure of the correlation energy detector can be made extremely simple from this point of view.
Another object of the present invention is to provide a radio communication apparatus which subjects each signal series which is described by I-Q orthogonal components and is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, wherein each finger includes a correlation energy detector so as to obtain the correlation values of the codes, the correlation energy detector detecting a magnitude of a correlation between a first signal series (Ii, Qi) described by I-Q orthogonal components and a predetermined second signal series (HJ), and comprising correlation computing means for computing correlation values (Iij, Qij) between the first signal series (Ii, Qi) and the predetermined second signal series (HJ), and root computing means for computing {{square root over ( )}(Iij2+Qij2)} as a root value of a sum of squares of the correlation values (Iij, Qij) obtained from the correlation computing means. According to the radio communication apparatus of the present invention, it is possible to simplify the structure of the apparatus by use of the correlation energy detector having a simple structure.
Still another object of the present invention is to provide a radio communication apparatus which subjects each signal series which is described by I-Q orthogonal components and is received via a multi-path and demodulated, to a Hadamard transform at each of fingers, by use of an M-ary quadrature coding scheme, obtains correlation values of codes, combines correlation values output from fingers which obtain valid correlation values, and demodulates a received signal based on a maximum correlation value of combined correlation values, the radio communication apparatus comprising a searcher which monitors a reception state by obtaining the correlation values of the codes for each path, and performs a path selection and a delay time adjustment with respect to each finger, the searcher including a correlation energy detector so as to obtain the correlation values of the codes, the correlation energy detector detecting a magnitude of a correlation between a first signal series (Ii, Qi) described by I-Q orthogonal components and a predetermined second signal series (HJ), and comprising correlation computing means for computing correlation values (Iij, Qij) between the first signal series (Ii, Qi) and the predetermined second signal series (HJ), and absolute value sum computing means for computing (|Iij|+|Qij|) as a sum of absolute values of the correlation values (Iij, Qij) obtained from the correlation computing means. According to the radio communication apparatus of the present invention, it is possible to simplify the structure of the apparatus by use of the correlation energy detector having a simple structure.